Histogram shape parameter ξ (Eqs. (4) and (5)) calculated for the different N_H bins in each region. The cases ξ> 0 and ξ< 0 correspond to the magnetic field oriented mostly parallel and perpendicular to the structure contours, respectively. For ξ ≈ 0 there is no preferred orientation. The displayed values of C_HRO and X_HRO were calculated from Eq. (6)and correspond to the grey dashed line in each plot.